Thaumatrope

A thaumatrope is an optical illusion toy that became popular in the 19th century. It is a circular disc with a different picture on each side, attached to two pieces of string. When the strings are twirled quickly, the two pictures appear to morph into one due to the optical illusion known as "persistence of vision". Persistence of vision is a phenomena in which in an object does not cease to exist for a short time after the rays of light following it have ceased to enter the eye. They are often seen as significant predecessors of motion pictures, particularly animation. It's invention is usually accredited to the British physician, John Ayrton Paris, although it is still debated until this day. It was first described in the 1827 book "Philosophy in Sport Made Science in Earnest". Others have contested that the thaumatrope was in fact invented later on in 1864 by the geologist, William Henry Fitton.

The video above shows a classic example of the images that might appear on a thaumatrope. A free bird on one side and a cage on the other gives the illusion that the the bird is infact trapped within the cage. Another well-known example is a carousel with a blank space in the middle on one side and a set of carousel horses on the other. The first set of thaumatropes became commercially available to the public in 1825, and came in sets of 12 or 18 discs. Their price point was criticised as being too expensive for the average working-class person, and so pirated copies soon began to trickle into the market. Original copies of the device are extremely rare to come by today. One single, original disc is held at the Cinémathèque Française in Paris, France.

Below are some other examples of images you might find on a thaumatrope -